The ants are not the initial cause of your plant's demise. They are most likely "farming" for aphids, which commonly attack bamboo plants. The sticky residue left behind from the sap-sucking pests generally attracts the ants. Neem oil is a great organic treatment for the aphids, and may help with the ants as well. Here is more information: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm